As shown in FIG. 1, the down-tilt of an antenna 10 is defined as the angle 11 between an imaginary horizontal line 12 traced from the top of the antenna and the direction 13 of the main lobe 14.
If said down-tilt angle is too low, then the antenna can provide coverage in an area located at considerable distance from the base station site; but, there is a risk of having more interference with the rest of base stations, and also there is risk of dropped call due to non-defined neighbour cells.
On the other hand, if the down-tilt angle is too high, the coverage of the cell can be too small, causing the rest of the neighbouring cells to carry too much traffic, thereby unbalancing the network load.
One of the problems in the optimization task in current networks is how to adjust the down-tilt of the antenna in order to provide an optimum coverage of the area covered by the base station where such antenna is located.
Several approaches aim at optimizing the area covered by a site, and include the possibility of adjusting the down-tilt angle of the base station antenna in order to do so.
For example, US 2006/0239224-A1 discloses a method of configuring a cell of a wireless communication system, in which a base station adjusts its access area so as improve resource utilization. It is dynamic method that responds in real time to traffic fluctuations. So the access area of the base station is adjusted selected on a traffic-based criterion.
Also, EP-1307066 discloses a method of optimizing the down-tilt angle of the antenna beam based on geometric data relating to the relative positions and orientations of base stations in a cellular network, and also based on measurements reports from mobile stations active with cells served by such base stations.
US 2006/0068849-A1 describes a method for controlling interference in CDMA networks which includes adjusting the coverage areas of a cell based on traffic load of the cells.